The FAA is investigating a close call between two United Airlines flights in Houston earlier this month and has put in place preventive measures in response to the incident, an official said Friday.

The incident occurred about 9:30 p.m. May 9 about two miles from George Bush Intercontinental Airport, Federal Aviation Administration officials said. Vancouver-bound United Flight 601, which had taken off on one runway, edged into the airspace reserved for flights that take off from another runway at the airport.

An air traffic controller instructed both planes – the other was United Flight 437 bound for Mexico City – to safely separate, FAA spokesman Lynn Lunsford said. The pair of Airbus A320s came within 0.87 miles laterally and 400 feet vertically. The required separation distance is being reviewed.

Lunsford declined to say what measures were put in place to prevent a similar incident.

Last month, the National Transportation Safety Board said, a more serious near-collision occurred at Newark Liberty International Airport in New Jersey. A United flight from San Francisco with 161 people on board and a Memphis, Tenn.-bound ExpressJet carrying 50 people were less than a football field apart laterally. The required separation distance in that case was two miles. The United flight aborted its landing to avoid an accident.

Collision avoidance has been a point of scrutiny at the FAA. Auditors have called for better tracking and studying of near-misses. Three years ago, the agency started doing more automatic reporting of such incidents.

The agency’s most recent safety report, released in September, said it investigated nearly 1,300 cases of so-called separation cases in fiscal 2012. Of those, 41 were deemed high-risk. Updated data were not immediately available.

FAA spokesman Ian Gregor said Friday that the agency was still investigating an April 25 case out of Hawaii in which a mainland-bound United flight made a sudden altitude change when an on-board system warned that it was too close to a U.S. Airways flight heading toward the islands.

Afterward, the FAA said it took immediate action to prevent a recurrence, but it has declined to provide details of any oversight or policy changes until the investigation is complete.

WPIX-TV reported that the FAA said it was also looking at a May 10 case involving two JetBlue flights at New York's John F. Kennedy International Airport. A controller asked the planes to separate after a just-departed flight came within about a half-mile of another flight executing a missed landing.